In production of semiconductor devices, an electron beam exposure technique receives a great deal of attention as a promising candidate of lithography capable of micro-pattern exposure at a line width of 0.1 μm or less. There are several electron beam exposure methods. An example is a variable rectangular beam method of drawing a pattern with one stroke. This method suffers many problems as a mass-production exposure apparatus because of a low throughput. To attain a high throughput, there is proposed a pattern projection method of reducing and transferring a pattern formed on a stencil mask. This method is advantageous to a simple repetitive pattern but disadvantageous to a random pattern such as a logic interconnection pattern in terms of the throughput, and a low productivity disables practical application.
To the contrary, a multi-beam system for drawing a pattern simultaneously with a plurality of electron beams without using any mask has been proposed and is very advantageous to practical use because of the absence of physical mask formation and exchange. What is important in using a multi-electron beams is the number of electron lens arrays used in this system. The number of electron lenses formed in an array determines the number of beams, and is a main factor which determines the throughput. Downsizing the electron lenses while improving the performance of them is one of keys to improving the performance of the multi-beam exposure apparatus.
Electron lenses are classified into electromagnetic and electrostatic types. The electrostatic electron lens does not require any coil core or the like, is simpler in structure than the electromagnetic electron lens, and is more advantageous to downsizing. Principal prior arts concerning downsizing of the electrostatic electron lens (electrostatic lens) will be described.
A. D. Feinerman et al. (J. Vac. Sci. Technol. A10(4), p. 611, 1992) disclose a three-dimensional structure made up of three electrodes as a single electrostatic lens by a micromechanical technique using a V-groove formed by a fiber and Si crystal anisotropic etching. The Si film has a membrane frame, membrane, and aperture formed in the membrane so as to transmit an electron beam. K. Y. Lee et al. (J. Vac. Sci. Technol. B12(6), p. 3,425, 1994) disclose a multilayered structure of Si and Pyrex glass fabricated by using anodic bonding. This technique fabricates microcolumn electron lenses aligned at a high precision. Sasaki (J. Vac. Sci. Technol. 19, p. 963, 1981) discloses an Einzel lens made up of three electrodes having lens aperture arrays. Chang et al. (J. Vac. Sci. Technol. B10, p. 2,743, 1992) disclose an array of microcolumns having Einzel lenses.
In the prior arts, if many aperture electrodes are arrayed, and different lens actions are applied to electron beams, the orbit and aberration change under the influence of the surrounding electrostatic lens field, and so-called crosstalk occurs in which electron beams are difficult to operate independently.
Crosstalk will be explained in detail with reference to FIG. 10. Three types of electrodes, i.e., an upper electrode 1, middle electrodes 2, and a lower electrode 3 constitute an Einzel lens. The upper and lower electrodes 1 and 3 are 10 μm in thickness and have 80-μm diameter apertures arrayed at a pitch of 200 μm. The middle electrodes 2 are 50 μm in thickness, have a cylindrical shape 80 μm in inner diameter, and arrayed at a pitch of 200 μm. The distances between the upper and middle electrodes 1 and 2 and between the middle and lower electrodes 2 and 3 are 100 μm. The upper and lower electrodes 1 and 3 receive a potential of 0 [V], middle electrodes 2 on central and upper rows B and A receive −1,000 [V], and middle electrodes 2 on a lower row C receive −950 [V]. The potential difference between adjacent electrodes is 50 [V]. When an electron beam having a beam diameter of 40 μm and an energy of 50 keV enters a central aperture from the left of the upper electrode 1, a downward shift angle Δθ of the electron beam becomes several ten μrad or more. A typical allowable value of the shift angle Δθ is 1 μrad or less. In this electrode arrangement, the shift angle exceeds the allowable range. That is, the electron beam is influenced by the surrounding lens field, and so-called crosstalk occurs, which must be solved.